Journal of Molecular Catalysis A: Chemical 370 (2013) 35 43

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Journal of Molecular Catalysis A: Chemical

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Magnetic properties and photocatalytic activity oLaFe0.9Mn0.1O3Zhi-Xian b,c,

a Department o hinab Beijing Instituc School of Mat a

a r t i c l

Article history:Received 28 AReceived in re21 December 2Accepted 23 DAvailable onlin

Keywords:Doped perovskire oxidesMagnetic catalystVisible light photocatalystMethyl orange (MO)

d Lactronvis abf the r phoThe eegrad

the magnetic property of the La0.8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3 was caused by the doubleexchange between Mn3+ and Fe3+, Mn3+ and Mn4+ as well as the defective state in them, the Ba-dopingLaFe0.9Mn0.1O3, i.e., La0.8Ba0.2Fe0.9Mn0.1O3, has higher magnetic property than that of LaFe0.9Mn0.1O3because of its higher Mn4+ content which favors the double exchange interaction between Mn4+andMn3+, and it has much higher photocatalytic activities than those of the LaFe0.9Mn0.1O3 due to its

4+

1. Introdu

Immobiland zeolitecic area athe high acnanophotocseparation as TiO2/ironphotocatalynetic partichave been sboth photoc[7]. For exa

CorresponUniversity of fax: +86 0351 Corresponogy, Beijing 10Institute of Te

E-mail add

1381-1169/$ http://dx.doi.ohigher oxygen vacancies, higher Mn content and higher visible light absorption. This new bifunctionalLa0.8Ba0.2Fe0.9Mn0.1O3 is extremely effective for the MO degradation, and it was easily separated byapplied magnetic eld and can be reusable and maintain relatively high activity.

2012 Elsevier B.V. All rights reserved.

ction

ization of photocatalysts on supports such as glass results in decreased activities due to the low spe-nd slow mass transfer. In order to take advantage oftivity of the suspended and dispersed semiconductoratalysts, the concept of magnetic photocatalysts withfunction was raised. Magnetic composite systems such

oxide [1], Ni/titania products [2], POM-based magneticsts [3], and anatase TiO2 nanoparticle coating on mag-les including barium ferrite [4], Fe3O4 [5], CoFe2O4 [6]tudied. The single-phase magnetic catalysts function asatalysis and separation were also started to be focusedmple, Tan developed three kinds of bismuth ferrites

ding author at: Department of Chemistry, Science Institute, NorthChina, Taiyuan, Shanxi 030051, PR China. Tel.: +86 0351 3921414;3921414.ding author at: Beijing Institute of Protective Materials and Technol-0072, PR China/School of Materials Science and Engineering, Beijingchnology, Beijing 100081, PR China.resses: zx wei@126.com (Z.-X. Wei), liujp@bit.edu.cn (J.-P. Liu).

(BiFeO3, Bi25FeO40, and Bi25FeO40BiFeO3) through a microwavehydrothermal method. Wei et al. also reported the magnetic andphotocatalytic properties of the perovskite-type SrTi0.1Fe0.9O3[8].

Since the visible light accounts for the largest portion (ca.46%) in the solar spectrum, the solar light-driven photocatalystsare desirable. Hence, development of the photocatalyst possess-ing of superparamagnetic property and visible-light activity (i.e.,bifunctional photocatalyst) has become an important topic in thephotocatalysis research today. Here, the superparamagnetic prop-erty is desirable for their applications considering their dispersionsand recycling.

Perovskite oxides with the general formula ABO3 are multi-functional materials. Indeed, they can even show novel couplingof multiple coexisting states, such as magnetism and super-conductivity, or ferroelectricity and ferromagnetism [9]. Further,substitution or doping at both A and B sites can change the com-position and symmetry of the oxides and create cations or oxygenvacancies, which have a major inuence on the band structuresand the photocatalytic behavior of these materials. Moreover, manyother properties such as adsorption [10] and magnetic properties[11] can also be designed and prepared by substitution or doping onboth A and B sites. A-site ion substitution/doping or oxygen content

see front matter 2012 Elsevier B.V. All rights reserved.rg/10.1016/j.molcata.2012.12.013 Weia,, Cai-Mei Xiaoa, Wei-Wei Zenga, Ji-Ping Liuf Chemistry, Science Institute, North University of China, Taiyuan, Shanxi 030051, PR Cte of Protective Materials and Technology, Beijing 100072, PR Chinaerials Science and Engineering, Beijing Institute of Technology, Beijing 100081, PR Chin

e i n f o

ugust 2012vised form012ecember 2012e 31 December 2012

a b s t r a c t

Perovskite La0.8Ba0.2Fe0.9Mn0.1O3 anpowder diffraction (XRD), scanning eleing sample magnetometer (VSM), UVtechniques. The magnetic properties oand they were also evaluated for thei(MO) under the sunlight irradiation. on the efciency of photocatalytic d/ locate /molcata

f La0.8Ba0.2Fe0.9Mn0.1O3 and

Fe0.9Mn0.1O3 were synthesized and characterized by X-ray microscopy (SEM), Fourier transform infrared (FT-IR), vibrat-sorption spectra and X-ray photoelectron spectroscopy (XPS)

La0.8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3 were measured,tocatalytic activity toward the degradation of methyl orangeffect of various parameters such as pH and irradiation timeation MO was studied. The experimental results show that

36 Z.-X. Wei et al. / Journal of Molecular Catalysis A: Chemical 370 (2013) 35 43

variation [12,13] and the change in crystallite size of the sample [14]can also change the magnetism. Therefore, perovskite-type oxideswith intrinsic visible photocatalytic activity and superparamag-netic property could be easily tunabled by many methods includingadding or dwell as the efforts have

In generNaTaO3, Basubstances,This is becaand Mn3+

are respons(0.0 x 1be designeA and B sLaFe0.9Mn0this study inphotocatalytype oxides

It is welimportant rnetic propethe effect alytic activLaFe0.9Mn0bustion mestudy. Herewith highetocatalytic methyl orauate the pLaFe0.9Mn0

2. Materia

2.1. Materi

La0.8Ba0acid solutiobe describFe(NO3)39Hwere addedreactor. Aftcontinuousviscous Lacrucible reat a heatinvolatilized of gases to After the aannealing tLa0.8Ba0.2FeLaFe0.9Mn0mole ratesthe stearic a

Mean vaand LaFe0.tion, respeaqueous sformed usLa0.8Ba0.2Fecompositioneutrality p

The crystalline phase structures of the obtained samples wasdetermined by X-ray diffractometer (Cu K = 1.54 A, 40 kV, 30 mA,2 from 10 to 80 ). FT-IR spectra were registered by using aNexus 870 FT-IR in KBr pellets. Scanning electron microscopy

(HITy of red ar (Hht abphoalysed w

(BE84.8 . Themeason sp

sorp

ll exueou

er tod thespenxper

pertry dm. ae in 7 51en 9:s we

lux. he so

by on She s

(%

= C0

C0 aner th

minal oxccorlizatsion.

lizat

COtiontrati

ults

D an

his sthe ahen jor iO. Hion doping a desirable component to the A and/or B site aschange in crystallite size of the sample. However, few

been carried out on that subject until now.al, there are several types of pervoskite structures likeTiO3, and LaCoO3 LaFeO3, etc. All the above-mentioned

the Mn ions doped LaFeO3 have magnetic property.use that the superexchange interaction between Mn3+

and the double exchange between Mn3+ and Mn4+

ible for the ferromagnetism of the LaMn(1x)FexO(3+y).0) [15]. Considering that the magnetic properties cand and prepared by substitution or doping on bothites, therefore, LaFe0.9Mn0.1O3 and the Ba-doping.1O3, i.e., La0.8Ba0.2Fe0.9Mn0.1O3 were prepared in

order to investigate the effect of the Ba-doping on thetic activity and magnetic properties of the perovskite-.l known that a preparation method can also play anole in the properties of the products including mag-rties and photocatalytic activities. In order to researchof the Ba doping on the magnetism and photocat-ity of LaFe0.9Mn0.1O3, La0.8Ba0.2Fe0.9Mn0.1O3 and.1O3 were prepared by the stearic acid solution com-thod [16] and characterized by many techniques in this, the combustion method can easily prepare powdersr specic surface areas, which is helpful to their pho-activity and superparamagnetic property. In addition,nge (MO) was chosen as a model pollutant to eval-hotocatalytic activity of La0.8Ba0.2Fe0.9Mn0.1O3 and.1O3 in this study.

ls and methods

al synthesis and characterization

.2Fe0.9Mn0.1O3 was synthesized by the stearicn combustion method. The detailed process coulded as follows: First, La(NO3)36H2O, Ba(NO3)2,2O and MnCl24H2O at the mole rates 0.8:0.2:0.9:0.1

in the excess molten stearic acid in a porcelain crucibleer that, the resulting mixture was heated and stirredly at 123 C for about 8 h to obtain fully homogeneousBaFeMnstearic acid solution. Then, the porcelainactor was placed on a hot plate increased to 500 Cg rate of 10 C/min in air. At this stage, the solutionand autoignited, with the evolution of a large volumeproduce loose powder, known as as-prepared powder.s-prepared powder was grinded and calcined at anemperature above 650 C for 1 h, black perovskite-type0.9Mn0.1O3 powders were obtained. In addition,.1O3 was also synthesized by the same method. The

of La(NO3)36H2O, Fe(NO3)39H2O, MnCl24H2O andcid are 1:0.9:0.1:8.lence of Fe and Mn ions in both La0.8Ba0.2Fe0.9Mn0.1O39Mn0.1O3 was determined by iodometric titra-ctively. The sample was dissolved in 6 M HCl

olution and titration of iodine formed was per-ing Na2S2O3 aqueous solution. Oxygen content in0.9Mn0.1O3/LaFe0.9Mn0.1O3 was estimated fromn and valences of cations in accordance with the chargerinciple.

(SEM) phologmeasutometeThe ligspectroXPS anequippenergy(BE = 2carbonwere emissi

2.2. Ad

In aMO aqin ordMO anthe sualytic e15 daychemis9:30 a.intenstion 3betwetuation96,000from tminedPrecisiusing tversion

(%)

whereand aft

Thechemicsured amineraexpres

Minera

whereadsorpconcen

3. Res

3.1. XR

In tcining that, wthe maand BaoxidatACHI, Model S-4800) was used to investigate the mor-the obtained powders. The magnetic properties weret room temperature using a vibration sample magne-H-10, Instrument Factory of Nanjing University, China).sorption spectrum was recorded with U-3010 UV-Vistometer (Hitachi, Japan) in the range of 200800 nm.is was performed by a PHI Quantera SXM apparatus,ith a standard Al K excitation source. The binding

) scale has been calibrated by measuring C 1s peakeV) from the ubiquitous surface layer of adventitious

amounts of La, Ba, Fe and Mn in the perovskite oxideured by P-4010 inductively coupled plasma atomicectrometer.

tion and photocatalytic experiments

periments, 5.0 g/L perovskite oxides was added to thes (3080 mg/L) and stirred in dark for some time,

achieve adsorptiondesorption equilibrium between La0.8Ba0.2Fe0.9Mn0.1O3/LaFe0.9Mn0.1O3. After that,sion was irradiated with sunlight and the photocat-iments were conducted in July 2011, over a continuousiod. All experiments were done out of the room ofepartment building in an open atmosphere between

nd 3.30 p.m. The sky is clear and the sunrays are verythis period in the city of Taiyuan (geographical loca-9 North Latitude and 112 33 00 East Longitude),30 a.m. and 3:30 p.m. where the solar intensity uc-re minimal, and the mean illumination of sunlight isAfter the photocatalysis, the powder was recoveredlution. The concentrations of MO solution were deter-UV-Visible spectrophotometer (Model 721, Shanghaicientic Instrument Co. Ltd., China) at max = 464 nmtandard curve. Adsorption and the photocatalytic con-) was calculated as follows:

CtC0

100

d Ct (mg/L) are the concentrations of MO solution beforee photocatalytic degradation, respectively.eralization of MO was measured by the decrease ofygen demand (COD) of the MO solution. COD was mea-ding to the standard dichromate titration method. Theion efciency of MO was estimated by the following

ion of MO (%) =(

1 CODtCOD0

) 100

D0 is the COD concentration after 5 mindesorption equilibrium, and CODt is the CODon at certain reaction time t, respectively.

and discussion

alysis

tudy, the La0.8Ba0.2Fe0.9Mn0.1O3 was obtained by cal-s-prepared powder, as shown in Fig. 1. It can be seencalcined at 650 C, the perovskite oxide is formed andmpurity in La0.8Ba0.2Fe0.9Mn0.1O3 is little La2O2CO3ere, the carbonation of La3+ would easily occur if theecomposition was performed in the CO2-containing

Z.-X. Wei et al. / Journal of Molecular Catalysis A: Chemical 370 (2013) 35 43 37

Fig. 1. XRD patterns of La0.8Ba0.2Fe0.9Mn0.1O3 powder calcined at 650 C for 1 h(a), 700 C for 1 h (b) and 800 C for 1 h (c).

gas-phase [17] (CO2 comes from the oxidation decomposition ofstearic acid or stearates). The minor peak of BaO is very low inten-sities (less tnegligible ierties. Withof the chardecrease anThe perovsexhibits ort

In additias-preparedcrystalline dened peaand MnO2as-preparedLa2O2CO3, powders. Wthe charactpeaks are dlittle La2O2La2O2CO3 aexhibits cub

Fig. 2. XRD paat 650 C for 1

Table 1Effect of calcination temperature of LaFe0.9Mn0.1O3 on photocatalytic activity.

Sample Temperature

Irradiation (%)

LaFe0.9Mn0.1

La0.8Ba0.2Fe0

3.2. Effect oand LaFe0.9M

In this sthe absenceperature ofthe degradaconcentrati(pH: not adtion rate onthe sunlighrespectivelyperature st

e prm

0.2Fed at gnetLa2Oas ted i

shoitionagnen cotic oFe0.9

oth is Baaric asamee Ba

are nn thtic ahan 1%), and this certies that the secondary phase hasnuence on the overall magnetic and catalytic prop-

a rise in the heating temperature, the intensitiesacteristic peaks of ABO3 increase, the La2O2CO3 peakd the BaO (PDF # 30-0143) peak gradually disappear.kite-type La0.8Ba0.2Fe0.9Mn0.1O3 calcained at 800 Chorhombic symmetry, with the space group of Pbnm.on, the LaFe0.9Mn0.1O3 was obtained by calcining the

powder. A clear transition from amorphous state tostate could be noticed in Fig. 2. The broad and poorlyks in Fig. 2a correspond to La2O2CO3 (PDF # 74-1144)(PDF # 04-0378) and LaOCl (PDF # 64-7261). So, the

powder obtained by the combustion is a mixture ofMnO2, LaOCl and signicant amounts of amorphousith a rise in the heating temperature, the intensities of

eristic peaks of ABO3 increase, and the MnO2 and LaOClisappeared. The major impurity in LaFe0.9Mn0.1O3 isCO3 after heating to 650 C (Fig. 2b). By 700 C for 1 h,lso disappeared. The perovskite-type LaFe0.9Mn0.1O3ic symmetry, with the space group of Pm3m.

with thAs

La0.8Bacalcinethe maof the [16] wdescribresultsIn addthe mone camagneand La

The700 Cthe steto the that thand Babetweemagnetterns of LaFe0.9Mn0.1O3: as-prepared powder (a), powder calcined h (b) and powder calcined at 700 C for 1 h (c).

calcined at In addit

are determspectroscoppresent a gvalues. Tho

In the focined at 70further chaproperties w

Fig. 3 shLaFe0.9Mn0and LaFe0.9leading to athe rough aface areas. the transpohave a porocatalytic ap( C) time (min)

O3 650 120 92.7700 120 88.3750 120 81.4

.9Mn0.1O3 650 20 30.5700 20 40.8750 20 12.2

f calcination temperature of La0.8Ba0.2Fe0.9Mn0.1O3n0.1O3 on photocatalytic activity

tudy, MO cannot be degraded by sunlight photolysis in of photocatalyst [8]. The effect of the calcination tem-

the La0.8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3 ontion of MO was investigated from 650 C to 750 C, at aon of 30 mg/L of MO and 5.0 g/L catalyst concentrationjusted). The results show that methyl orange degrada-

La0.8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3 undert reaches the maximum value at 700 C and 650 C,

(see Table 1). This indicates that the calcination tem-rongly affects the photocatalytic activity, in agreementevious results [18].entioned above, the major impurity in0.9Mn0.1O3 calcined at 700 C and LaFe0.9Mn0.1O3650 C are La2O2CO3. Can it have any intrinsic effect onic or catalytic properties? So, the photocatalytic activity2CO3 prepared by the stearic acid solution combustionested according to the same experimental methodn Section 2.2 (5.0 g/L La2O2CO3). The experimentalw that, the La2O2CO3 has no catalytic performance., La3+, O2 and C4+ are non-magnetic ions, and hencetic interactions between them are absent. Therefore,nclude that the La2O2CO3 has not any effect on ther catalytic properties of the La0.8Ba0.2Fe0.9Mn0.1O3Mn0.1O3.er impurity in La0.8Ba0.2Fe0.9Mn0.1O3 calcined atO. So, the photocatalytic activity of the BaO prepared bycid solution combustion [16] was also tested according

experimental method. The experimental results showO also has no catalytic performance. In addition, O2

on-magnetic ions, and hence the magnetic interactionsem are absent. Therefore, the BaO has no effect on thend catalytic properties of the La0.8Ba0.2Fe0.9Mn0.1O3700 C.ion, the amounts of metals in La0.8Ba0.2Fe0.9Mn0.1O3ined by inductively coupled plasma atomic emissiony, and the values of the mass percent La, Ba, Fe, Mn

ood balance between the theoretical and experimentalse results are shown in Table 2.llowing experiments, the La0.8Ba0.2Fe0.9Mn0.1O3 cal-0 C and the LaFe0.9Mn0.1O3 calcined at 650 C wereracterized. Moreover, their magnetic and photocatalytic

ere further investigated.ows SEM images of the La0.8Ba0.2Fe0.9Mn0.1O3 and.1O3. It could be seen that the La0.8Ba0.2Fe0.9Mn0.1O3Mn0.1O3 are almost-spherical nano-agglomerates,

rough surface and the presence of pore structure. Here,nd porous surface of the powders could enhance the sur-Moreover the porous structure is believed to facilitatertation of reactant molecules. Therefore, the powdersus structure with a rough surface which is suitable forplications [19].

38 Z.-X. Wei et al. / Journal of Molecular Catalysis A: Chemical 370 (2013) 35 43

Table 2Inductively coupled plasma atomic emission spectroscopy analyses.

Perovskite oxide Theoretical (%) Real (%)

La Ba Fe Mn La Ba Fe Mn

La0.8Ba0.2Fe0.9Mn0.1O3 46.7 11.5 21.1 2.3

Fig. (a) an

Table 3Magnetic dataat different tem

Temperatur

650 700 800

3.3. Magne

The magcined at difas shown imagnetizatwere given calcined atferromagnesaturated mture decrea650 C. Thenet (50 mmin Fig. 4d.

The magLaFe0.9Mn0the range oters were gicalcined at ferromagnesaturated mdecreases, a

Table 4Magnetic datadifferent temp

Temperatur

600650700 750

h the peae (slinitytisme actcreasraturf th0.2Fet stu3. SEM micrograph of La0.8Ba0.2Fe0.9Mn0.1O3- calcined at 700 C for 1 h. (30,000)

of La0.8Ba0.2Fe0.9Mn0.1O3 obtained by calcining as-prepared powderperature for 1 h.

es (C) Hc (Oe) Mr (emu/g) Ms (emu/g)

56.86 10.24 41.9420.93 4.36 19.3189.69 4.30 10.99

tic properties

Witteristicincreascrystalmagnemay bthe detempestate oLa0.8Bapresennetic properties of the La0.8Ba0.2Fe0.9Mn0.1O3 cal-ferent temperatures are investigated in air ambience,n Fig. 4. The magnetic parameters such as saturationion Ms, coercivity Hc and remanent magnetization Mrin Table 3. One can see that the La0.8Ba0.2Fe0.9Mn0.1O3

different temperatures all exhibit room-temperaturetism and have lower coercivities and remanences. Theagnetization (Ms) increases as annealing tempera-

ses, and attains the peak value (Ms = 41.94 emu/g) at response of the powder calcined at 700 C to a mag-

50 mm 10 mm, surface eld of 3000 G) is shown

netic hysteresis loops measured in air ambience for the.1O3 obtained by calcining the as-prepared powder inf 600750 C are shown in Fig. 5. The magnetic parame-ven in Table 4. It can be seen that the LaFe0.9Mn0.1O3different temperatures also exhibit room-temperaturetism and have lower coercivities and remanences. Theagnetization (Ms) increases as annealing temperaturend attains the peak value (Ms = 13.52 emu/g) at 600 C.

of LaFe0.9Mn0.1O3 obtained by calcining as-prepared powder aterature for 1 h.

e (C) Hc (Oe) Mr (emu/g) Ms (emu/g)

44.69 1.72 13.5248.06 1.74 12.8378.71 0.90 5.1495.11 0.11 0.58

defect formdefects gening as largeis in agreem

It is repphotocatalycoercivity aaggregationlysts) afteroriginal rearedispersedLaFe0.9Mn0tion magnetemperaturremanent mis needed tof great inThe La0.8Bation can bFig. 4d, theprepared p(50 mm 5higher satu

In additsolid state tion magneshows that in the prop

In orderLa0.8Ba0.2Fe40.6 10.9 18.2 2.2

d LaFe0.9Mn0.1O3- calcined at 650 C for 1 h (100,000) (b).

increasing temperature, the intensities of the charac-ks of the La0.8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3ee Figs. 1 and 2), indicating the increase in the

and the decrease in the defects. Therefore, the ferro- of the La0.8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3ivated by defects induced after calcination, wherease of ferromagnetism with the increase of calcinatione (see Figs. 4 and 5) is possibly due to a less-defectivee La0.8Ba0.2Fe0.9Mn0.1O3- and LaFe0.9Mn0.1O3. The0.9Mn0.1O3 and LaFe0.9Mn0.1O3 particles in thedy have probably been sintered and accompanied byation at particle/particle interfaces. These interfacialerate ferromagnetism in these samples, possibly by act-

volume magnetic polarons which couple the spins. Thisent with that reported by Wongsaprom et al. [20].orted that the superparamagnetic property of thest or the higher saturation magnetization, the lowernd remanent magnetization can largely reduce their

(especially for the superparamagnetic photocata- they were separated by applied magnetic eld from

ction solution, so such photocatalysts can be easily

in a solution for reuse [18,21]. Compared with the.1O3, the La0.8Ba0.2Fe0.9Mn0.1O3 has higher satura-tization (Ms) when they were calcined at the samees (see Tables 3 and 4). However, the coercivity andagnetization show irregular changes. Further work

o achieve a thorough understanding, and this will beterest to researchers in the eld of magnetic oxides.0.2Fe0.9Mn0.1O3 with higher saturation magnetiza-e easily separation from the solution. As shown in

La0.8Ba0.2Fe0.9Mn0.1O3 obtained by calcining the as-owder at 700 C can be easily attracted with a magnet0 mm 10 mm, surface eld of 3000 G) owing to itsration magnetization.ion, compared with the LaFe0.9Mn0.1O3+ prepared byreaction [15], the LaFe0.9Mn0.1O3 has higher satura-tization (Ms) and the lower coercivity in this study. Thisa preparation method can indeed play an important roleerties of the products.

to analyze the origin of the ferromagnetism of the0.9Mn0.1O3 and LaFe0.9Mn0.1O3, XPS analysis was

Z.-X. Wei et al. / Journal of Molecular Catalysis A: Chemical 370 (2013) 35 43 39

Fig. 4. Field dependence of magnetization of La0.8Ba0.2Fe0.9Mn0.1O3- calcined at different temperatures: 650 C (a), 700 C (b), 800 C (c) and response ofLa0.8Ba0.2Fe0.9Mn0.1O3- calcined at 700 C to a magnet (d).

Fig. 5. Field detemperatures:

performed.LaFe0.9Mn0with a dist719.3 eV is the similar rFe elementare Fe3+ sta

Fig. 7 shows the Mn 2p3/2 spectra of the La0.8Ba0.2Fe0.9Mn0.1O3and LaFe0.9Mn0.1O3. It can be seen that the Mn 2p3/2 of

re broad and asymmetric toward the high binding energyeak proc

eV), 0.8Ba

eV), This

La0.them aside. Pthesis (640.4the La(641.4tively. of thependence of magnetization of LaFe0.9Mn0.1O3 calcined at different 600 C (a), 650 C (b), 700 C (c) and 750 C (d).

Fe 2p XP spectra of the La0.8Ba0.2Fe0.9Mn0.1O3 and.1O3 are shown in Fig. 6. In Fig. 6a, the peak at 710.3 eVinct large and low intensity satellite peak at aboutcharacteristic of Fe3+ in perovskite oxides [22], whileesults have been observed in Fig. 6b. This indicates that

s of the La0.8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3te.

be emphasyields ambMn4+ specenergy valmine the cLa0.8Ba0.2Fe

In concLa0.8Ba0.2FeMn3+ and exist the pFe3+, and h(0 x 0.5)and hence one can exLa0.8Ba0.2Feble exchangin them, re

Fig. 6. Fe 2p XP spectra of La0.8Ba0.2Fe0.9Mn0.1O3 (a) anintensities were evaluated by applying a peak syn-edure that includes three components, namely Mn2+

Mn3+ (641.3 eV), Mn4+ (642.3 eV) and a satellite for0.2Fe0.9Mn0.1O3 [23] and the Mn2+ (641.0 eV), Mn3+

Mn4+ (642.6 eV) for the LaFe0.9Mn0.1O3, respec- demonstrates the presence of Mn2+, Mn3+and Mn4+

8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3. It shouldized at this point that the deconvolution methodiguity in the recognition of the Mn2+, Mn3+ andies due to the small differences in their bindingues [2325]. Hence, it is difcult for one to deter-ontent of the Mn2+, Mn3+ and Mn4+ species of the0.9Mn0.1O3/LaFe0.9Mn0.1O3.lusion, the magnetic Fe, Mn elements of the0.9Mn0.1O3 and LaFe0.9Mn0.1O3 are Fe3+, Mn2+,Mn4+states. It is reported [26] that LaFe0.5Mn0.5O3ossibility of double exchange between Mn3+ andence it has the ferromagnetism, and La1xSrxMnO3

has double exchange interaction of Mn4+ and Mn3+

it has the superparamagnetic behavior [27]. Therefore,plain that the origin of the ferromagnetism of the0.9Mn0.1O3 and LaFe0.9Mn0.1O3 is due to the dou-e interaction between Mn3+ and Fe3+, Mn4+ and Mn3+

spectively. After doping Ba for La in LaFe0.9Mn0.1O3,d LaFe0.9Mn0.1O3 (b).

40 Z.-X. Wei et al. / Journal of Molecular Catalysis A: Chemical 370 (2013) 35 43

Fig. 7. Mn 2p3/2 XP spectra of La0.8Ba0.2Fe0.9Mn0.1O3 (a) a

Mn4+ ions are created due to charge balance, i.e., the Ba substi-tution induced the increase in Mn4+ content which favors thedouble exchange interaction of Mn4+ and Mn3+. Therefore, theLa0.8Ba0.2Feof the LaFe0

3.4. The UV

The ULa0.8Ba0.2Fecalcined atpared withhas slightranges, indof the La0Ba2+ in La La0.8Ba0.2Feirradiation tocatalyst. the La0.8Bto be estimabsorption.

Fig. 8. UVvis

3.5. AdsorpLa0.8Ba0.2FeMO

Adso0.2Fe

he ro0.2Fed atig. 9

rapwith0.8Bain acribe0.2Fetion

valFe0.9This tion e0.9Mther,ic d

co0.2Fe

for0.9Mn0.1O3 has higher magnetic property than that.9Mn0.1O3.

vis diffuse reectance spectra

Vvis diffuse reectance spectra of the0.9Mn0.1O3 calcined at 700 C and LaFe0.9Mn0.1O3

650 C are recorded and illustrated in Fig. 8. Com- the LaFe0.9Mn0.1O3, the La0.8Ba0.2Fe0.9Mn0.1O3ly higher absorption between the 400800 nmicating that visible light (460800 nm) absorption.8Ba0.2Fe0.9Mn0.1O3 slightly increases by dopingsite, i.e., it has higher visible light adsorption. The0.9Mn0.1O3 could be excited under visible lightand could be developed a new visible light pho-In addition, it can be seen that the band gaps ofa0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3 are hardated due to the lack of sharpness in the optical

3.5.1. La0.8BaMO

At tLa0.8Bacalcine(see Ftrationvalue for Lavalue are asLa0.8Baadsorplibriumand Latively. adsorpthe LaF

FurcatalytorangeLa0.8Ba5 mg/L spectra of LaFe0.9Mn0.1O3 (a) and La0.8Ba0.2Fe0.9Mn0.1O3 (b).

shown in Fincreased wand then reLa0.8Ba0.2FerespectivelLa0.8Ba0.2Feence of LaLa0.8Ba0.2FeLaFe0.9Mn0

3.5.2. KinetAt room

centration concentratiwith a xeddation efcfrom 30 to nd LaFe0.9Mn0.1O3 (b).

tive and photocatalytic activities of0.9Mn0.1O3 and LaFe0.9Mn0.1O3 for the removal of

rptive and photocatalytic activities of0.9Mn0.1O3 and LaFe0.9Mn0.1O3 for the removal of

om temperature condition, adsorptive properties of the0.9Mn0.1O3 calcined at 700 C and LaFe0.9Mn0.1O3

650 C for the removal of MO were investigated). The experimental results show that MO concen-idly decreases and slowly reaches an equilibrium

increasing adsorption time in approximately 4 min0.2Fe0.9Mn0.1O3, while MO reaches an equilibriumpproximately 30 min for LaFe0.9Mn0.1O3, whichd to the adsorption of MO on the surface of the0.9Mn0.1O3/LaFe0.9Mn0.1O3. A further increase oftime has a negligible effect on the MO adsorption. Equi-ue of adsorption of MO with La0.8Ba0.2Fe0.9Mn0.1O3Mn0.1O3 is 76.3% and 53.0% (Fig. 9a and b), respec-shows that the La0.8Ba0.2Fe0.9Mn0.1O3 has higher MOcapacity and a higher adsorption velocity than those ofn0.1O3.

the effect of irradiation time on the photo-egradation of MO was investigated at methylncentration of 30 mg/L at pH 1.0 with the0.9Mn0.1O3/LaFe0.9Mn0.1O3 concentration of

a sufcient period of time. The results are also

ig. 9. Fig. 9 shows that MO degradation rate rapidlyith increasing irradiation time in the initial stage,

ached an equilibrium value of 99.8% for 16 min for the0.9Mn0.1O3 and 98.2% for 3 h for the LaFe0.9Mn0.1O3,y. The degradation velocity of MO in the presence of0.9Mn0.1O3 was much faster than that in the pres-Fe0.9Mn0.1O3. Hence, the catalytic activity of the0.9Mn0.1O3 was much higher than that of the.1O3.

ics of the photocatalytic degradation temperature, the effect of the methyl orange con-on degradation efciency was studied by varying theon from 30 mg/L to 100 mg/L under sunlight irradiation

pH (1.0). The experimental results show that the degra-iency decreases with an increase in concentration of MO80 mg/L.

Z.-X. Wei et al. / Journal of Molecular Catalysis A: Chemical 370 (2013) 35 43 41

O for La0.8Ba0.2Fe0.9Mn0.1O3 (a) and LaFe0.9Mn0.1O3 (b).

Co= 100 mg/L

Co= 75 mg/L

Fig. 10. Secon(b).

The expewhich in its

1Ct

= 1C 0

+ k

where C0adsorptiontime t and kplots of phconcentratiLaFe0.9Mn0linear ttinthe above eapparent raare shown apparent raof MO.

Table 5Kinetic paramLa0.8Ba0.2Fe0.9M

Ct (mg/L)

8050 30Fig. 9. Effect of adsorption and sunlight irradiation time on the degradation of M

0.5

0.6

0.7

0.8

0.9

C0=80 mg/L

C0=50 mg/L

C0=30 mg/L1/Ct

a

0.2

0.3

0.4

0.5

1/Ct

b5 10 150.1

0.2

0.3

0.4

Irradiation time (min)

0

0.0

0.1

d-order kinetic plots of photocatalytic degradation of MO at different initial concentratio

rimental data was subjected to second-order-kinetics, usual form is given by

app t (1)

is the concentration value of MO of thedesorption equilibrium, Ct is the concentration atapp is the apparent rate constant. Second-order kineticotocatalytic degradation of MO at different initialon in the presence of the La0.8Ba0.2Fe0.9Mn0.1O3 and.1O3 are shown in Fig. 10 and Fig. 11, respectively. Ag of the data between 1/Ct and irradiation time (t) toquation conrmed the applicability of this model. Thete constant (kapp) and the correlation coefcient valuesin Table 5 and Table 6, respectively. It is seen that thete constants decrease with increasing concentrations

eters of second-order kinetic model for MO degradation byn0.1O3 .

Reaction kinetic equation kapp (mol1 L min1) R

1/Ct = 0.0880 + 1.01 102t 1.01 102 0.99891/Ct = 0.0317 + 2.03 102t 2.03 102 0.99671/Ct = 0.0083 + 3.5 102t 3.5 102 0.9986

In this stpore diameare 9.1 m2/ing value i Co= 50 mg/L30 60 90 12 0

Irr adiation t ime ( min)

n in the presence of La0.8Ba0.2Fe0.9Mn0.1O3 (a) and LaFe0.9Mn0.1O3

udy, the specic surface area, pore volume and averageter of the La0.8Ba0.2Fe0.9Mn0.1O3 calcined at 700 Cg, 0.05 cm3/g, 22.9 nm, respectively, the correspond-n LaFe0.9Mn0.1O3 calcined at 650 C are 15.8 m2/g,

Fig. 11. Effect of pH on degradation efciency of MO.

42 Z.-X. Wei et al. / Journal of Molecular Catalysis A: Chemical 370 (2013) 35 43

Table 6Kinetic parameters of second-order kinetic model for MO degradation byLaFe0.9Mn0.1O3.

Ct (mg/L)

100 7550

0.08 cm3/g surface areare lower help to exof the La0.of Fe andLa0.8Ba0.2Fecorrespondtively. Thesoxygen vacof the LaFestrong absocatalyst. Whtion of radiparticular sas the hydrthe photocacontains moble light reghence, the Lalytic activiand LaFe0.9ions with vatocatalytic Mn2+ and Melectronhooxygen adsrecombinatmoting the the increasthat a fractiand the samcould induccatalytic pr

In conLa0.8Ba0.2Fecies, higheThe La0.8Bamagnetic pphotocatalyproperties oxides inde

In the focined at 700its photoca

3.6. Effect o

The pH parameter tocatalytic a1.0 to 10.5.the photocasolution. Thincrease of pdecreases q

. Min.2Fe0.9

ing 0.2Fen of La0.8charorbinilabling torbenegatid La0here

inera

the 30 msunlOD rction

100 that0.2Fe0.9Mn0.1O3 under sunlight irradiation. Additionally,neralization rate is slower than the degradation rate by com-

Figs. 9 and 12. This suggests that the chromophore of MOlar was easily destructed for the sunlight photocatalytication by the La0.8Ba0.2Fe0.9Mn0.1O3, and then the degrada-termediates with small molecular were further mineralizedand H2O.

generation and reusability of La0.8Ba0.2Fe0.9Mn0.1O3

h the aim of exploring the potential reutilization ofa0.8Ba0.2Fe0.9Mn0.1O3 as photocatalyst for the MOation, thermal regeneration tests were carried out byng the exhausted La0.8Ba0.2Fe0.9Mn0.1O3 at differentReaction kinetic equation kapp (mol1 L min1) R

1/Ct = 0.0333 + 1.33 103t 1.33 103 0.99091/Ct = 0.0351 + 2.13 103t 2.13 103 0.99851/Ct = 0.0372 + 3.84 103t 3.84 103 0.9975

and 19.8 nm, respectively. Obviously, the specica and pore volume of the La0.8Ba0.2Fe0.9Mn0.1O3than those of the LaFe0.9Mn0.1O3. That does notplain the better adsorption and catalytic activities8Ba0.2Fe0.9Mn0.1O3. In addition, the mean valence

Mn and the value for oxygen vacancies () in0.9Mn0.1O3 is 3.05 and 0.08, respectively, while theing value in LaFe0.9Mn0.1O3 is 2.94 and 0.03, respec-e results show that La0.8Ba0.2Fe0.9Mn0.1O3 has higherancies and the mean valence of Fe and Mn than those0.9Mn0.1O3. The oxygen vacancies can bring on therption of OH, H2O or molecular O2 at the surface of theen the electronhole pairs are generated after absorp-ation by the catalyst, they could be trapped by thesepecies and thus can generate some active species suchoxyl radicals and adsorbed oxygen [28], resulting intalytic degradation of MO. The La0.8Ba0.2Fe0.9Mn0.1O3re oxygen vacancies and higher absorption in the visi-ion than those of the LaFe0.9Mn0.1O3 (see Fig. 8), anda0.8Ba0.2Fe0.9Mn0.1O3 has higher adsorption and cat-ty. Further, Mn element in the La0.8Ba0.2Fe0.9Mn0.1O3Mn0.1O3 is Mn2+, Mn3+ and Mn4+ state. Hence, Mnriable valance could exert signicant inuence on pho-action. Due to the fact that Mn4+ is more stable thann3+, Mn4+ can serve as electron trapper to separate thele pairs, while Mn3+ and Mn2+ can give electrons to the

orbed on the surface of the catalyst, thus prohibiting theion of the electronhole pairs, hence signicantly pro-photocatalytic activity. Further, barium doping inducede in Mn4+ content in La0.8Ba0.2Fe0.9Mn0.1O3 becauseon of trivalent La ions is substituted by divalent ion Bae fraction of Mn3+ is transformed to Mn4+. Hence, thise that the La0.8Ba0.2Fe0.9Mn0.1O3 has higher photo-operty than that of LaFe0.9Mn0.1O3.clusion, the higher catalytic activity of the0.9Mn0.1O3 is due to its higher oxygen vacan-r Mn4+ content and higher visible light absorption.0.2Fe0.9Mn0.1O3 is the photocatalyst possessing ofroperty and visible-light activity, i.e., bifunctionalst. This also indicates that the adsorption and magneticas well as photocatalytic activities of the perovskiteed can be designed by doping elements on the La sites.llowing experiments, the La0.8Ba0.2Fe0.9Mn0.1O3 cal-C was used as the magnetic visible photocatalyst and

talytic properties were further investigated.

f solution pH

of the aqueous solution is an important controllingin photocatalytic process. The effect of pH on the pho-

Fig. 12La0.8Ba0

DurLa0.8Bareactiobate (heteroof adsbe avaaccordof adsThe nchargetions. T

3.7. M

At cies ofunder that Cof reawithinshowsLa0.8Bathe miparingmolecudegradtion into CO2

3.8. Re

Witthe Ldegradcalcinictivity of the La0.8Ba0.2Fe0.9Mn0.1O3 was tested from The results are shown in Fig. 11. It can be seen thattalytic activity is largely dependent on the pH of thee degradation efciency decreases quickly with theH, when the pH exceeds 5.0. The degradation efciencyuickly. The optimum pH is 1.0.

temperaturLa0.8Ba0.2Fephotocatalyrate of MOof MO, theerated La0eralization of 10 mL 30 mg L1 MO in the presence ofMn0.1O3 under sunlight irradiation.

photocatalysis, adsorption occurred rst when the0.9Mn0.1O3 was dispersed in MO solution. In theadsorption, the charges of adsorbent (MO) and adsor-Ba0.2Fe0.9Mn0.1O3) played an important role. Thege between the adsorbent and adsorbate is in favorg reaction. At acidic conditions, more protons coulde to protonate the La0.8Ba0.2Fe0.9Mn0.1O3 surfaceo recent studies [29], which led to positive chargest surface, while MO carry negative charges (SO3).vely charged MO was adsorbed on the positively.8Ba0.2Fe0.9Mn0.1O3 surface via electrostatic interac-by acidic condition is helpful to the degradation of MO.

lization of MO

room temperature condition, COD removal efcien-g L1 MO solutions by the La0.8Ba0.2Fe0.9Mn0.1O3

ight irradiation are shown in Fig. 12. It can be seenemoval efciencies were increasing with the increase

time, 88.2% COD removal efciency was achievedmin reaction time for the La0.8Ba0.2Fe0.9Mn0.1O3. This

MO molecule can be effectively mineralized by thees. The experimental results show the regenerated0.9Mn0.1O3 calcined at 700 C for 1 h has highertic activity for the MO degradation, the decoloration

reaches to 93.2%. Fig. 13 shows the FT-IR spectra exhausted La0.8Ba0.2Fe0.9Mn0.1O3 and the regen-.8Ba0.2Fe0.9Mn0.1O3 calcined at 700 C for 1 h. A

Z.-X. Wei et al. / Journal of Molecular Catalysis A: Chemical 370 (2013) 35 43 43

Fig. 13. FT-IRexhausted La0

comparisonpeaks of Mthe degraddegradationadsorption,efcient ph

In additilent photocreconvertederation cycapproximatcause photoarea. This cthe results is reusable La0.8Ba0.2Feapplicationfrom air.

For peronetic charasubstitutionin crystallitdesign andnetic nature

4. Conclus

The La0.8thesized byexhibit roocivity (Hc) of the La0.8La-site, andthat of thecies and higTheir ferro

between Mn3+ and Fe3+, Mn3+ and Mn4+ as well as the defec-tive state in La0.8Ba0.2Fe0.9Mn0.1O3/LaFe0.9Mn0.1O3. Further,the La0.8Ba0.2Fe0.9Mn0.1O3 can be easily recycled by an exter-nal magnetic eld and redispersed in a solution for reuse for itshigher saturation magnetization, lower coercivity (Hc) and rema-nent magnetization (Mr). The optimal conditions were an initialmethyl orange concentration of 30 mg L1, at pH 1.0 with theLa0.8Ba0.2Fe0.9Mn0.1O3 concentration of 5 g L1 for 16 min sun-light irradiation with good repeated use of the catalyst. This studycould point out a potential way to develop new and more activemagnetic perovskite-type photocatalysts for the wastewater treat-ment.

wled

s pron Shl of N

nces

hang,09) 45

JiangQiu, Y. Lee,

(2004eydo. Li, J.N. Liu, E. Chen11) 13. Hwaamm

. Han,426. Canoernhang80.. Liu, San, S.X. de Lims. 105. Wei, . Milt96) 57. Chen13 (20

Lpealgo, p://dxWong506.1. Ao, J. Giraueclerc spectra: MO (a), regenerated La0.8Ba0.2Fe0.9Mn0.1O3 (b) and.8Ba0.2Fe0.9Mn0.1O3 (c).

of Fig. 13a and b replies that all the characteristicO disappear or are very weak in Fig. 13b, indicatingation of MO is mainly related to the photocatalytic

on the La0.8Ba0.2Fe0.9Mn0.1O3 rather than only and La0.8Ba0.2Fe0.9Mn0.1O3 did play a role of anotocatalyst.on, the regenerated La0.8Ba0.2Fe0.9Mn0.1O3 has excel-atalytic activity for the degradation of MO and it can be

into better photocatalyst for reuse. After four regen-les, the MO degradation was found to decrease onlyely 6.3% (from 93.2% to 86.9%). Heat treatment mightcatalyst aggregation and a decrease in specic surfaceould explain the loss of catalytic capacity. Howeverabove still indicate that the La0.8Ba0.2Fe0.9Mn0.1O3and maintain relatively high activity. Therefore, the0.9Mn0.1O3 is potentially employable in practicals under mild condition such as natural light and oxygen

vskite-type oxides ABO3, the photocatalysis and mag-cteristics could be easily tunabled by appropriates or doping at the A and B site as well as the changese size, etc. As a result of the combined effect, one can

prepare perovskite-type oxides with superparamag- and visible photocatalytic activity.

ions

Ackno

ThiTaiyuaCounci

Refere

[1] L. Z(20

[2] J.H.[3] W. [4] S.W

16 [5] D. B[6] X.Y[7] S.Q[8] H.X

(20[9] H.Y

[10] R. H[11] L.A

261[12] L.A

Hyp[13] N. Z

77[14] K.L

Du[15] O.F

Phy[16] Z.X[17] V.G

(19[18] X.Q

C 1[19] F.J.

Hidhtt

[20] K. 162

[21] Y.H[22] J.M

G. L

Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3 can be syn-

stearic acid solution combustion method. They allm-temperature ferromagnetism and have lower coer-and remanent magnetization (Mr). The magnetismBa0.2Fe0.9Mn0.1O3 is improved after doping Ba at

it has much higher photocatalytic activity than LaFe0.9Mn0.1O3 due to its higher oxygen vacan-her Mn4+ content and higher visible light absorption.magnetism were caused by the double exchange

[23] K. Barbar[24] C. Morill

217221[25] S. Valenc[26] K. Ueda, Y[27] S. Daengs

rung, S. M[28] Z.X. Wei

159616[29] F. Shimojgements

ject was supported by Science and Technology Item inanxi (Nos. 120247-13) and the Natural Science Fundorth University of China.

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Magnetic properties and photocatalytic activity of La0.8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O31 Introduction2 Materials and methods2.1 Material synthesis and characterization2.2 Adsorption and photocatalytic experiments

3 Results and discussion3.1 XRD analysis3.2 Effect of calcination temperature of La0.8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3 on photocatalytic activity3.3 Magnetic properties3.4 The UVvis diffuse reflectance spectra3.5 Adsorptive and photocatalytic activities of La0.8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3 for the removal of MO3.5.1 Adsorptive and photocatalytic activities of La0.8Ba0.2Fe0.9Mn0.1O3 and LaFe0.9Mn0.1O3 for the removal of MO3.5.2 Kinetics of the photocatalytic degradation

3.6 Effect of solution pH3.7 Mineralization of MO3.8 Regeneration and reusability of La0.8Ba0.2Fe0.9Mn0.1O3

4 ConclusionsAcknowledgementsReferences